In the forming of metal tops for furniture pieces such as tables and, more commonly, cabinets such as filing cabinets, it has been common practice to put a metal blank into a press and to then bend down the edges to form the sides for the top. The edges would then be joined by welding to form the corners which would then be ground to remove the traces of the weld and to shape the corner. The manufacturing of tops by this procedure was very labor intensive and was also subject to a high scrap rate due to the difficulty in welding and grinding of the thin metal corners. The metal would often be burned in the welding process and/or crack in the grinding process and, even more frustrating, an apparently acceptable top would, after painting and being installed on a piece of furniture, crack in shipment to a customer due to the vibration produced in the moving process. The product would arrive at the customer having one or more cracked corners on the furniture top and would be unacceptable, potentially causing bad will with the customer.
Furniture tops have also been prepared using a combined bending and drawing operation. However, the corners of the drawn tops had to be rounded because of the stresses involved in the drawing process. Tops prepared in this manner were only suitable for special applications where rounded corners could be tolerated. They could not be used on cabinets and particularly file cabinets where sharp corners are needed in order to allow the cabinets to be butted together into a substantially unbroken line.
Conventional wisdom in the stamping industry dictates that in order to make drawn steel parts, certain restrictions related to radius of corners and depth of draw must apply. Deeper draws and smaller radii beyond these limits would require secondary draws and auxiliary operations, respectively. Also, imperfections such as shocklines created by the draw process are unavoidable and must be tolerated.
The formation of corners for metal tops by drawing has been long desired in the metal furniture industry. The progress in this field has been substantially limited by the inability to draw the metal far enough to make acceptable corners. As a result of considerable effort, a "rule-of-thumb" for a single stage draw was accepted that one could not draw metal longer than eight times its thickness. For example, a 0.031 inch thick piece of metal could only be drawn 0.250 inch which was too short for use in a furniture top.